This invention relates to nonlinear circuits for driving inductive loads and in particular a switching driver circuit for use in a fuel injection system of an internal combustion engine.
Previous driver or solenoid control circuits for injectors for internal combustion engines utilized linear solenoid driving circuits to generate and deliver a rapid change in the rise current of a coil of a solenoid valve associated with a fuel injector. These linear driver circuits and/or systems used feedback techniques to control the level of injector current and often employed a boost voltage network to produce an increased voltage level that periodically overdrove the injector coil. These prior systems work adequately, however, they are often characterized as having high power consumption. In addition, large enclosures are often associated with these systems since it is necessary to dissipate the excess heat generated. The present invention offers a solution to the above problems by providing a driver circuit which functions in a switching mode of operation.
Accordingly, the invention comprises:
A solenoid control unit for controlling the operation of at least one fuel injector of an engine, each injector of the type having a coil. The solenoid control unit is responsive to metering signals generated by an electronic control unit in response to at least one engine parameter, and wherein each fuel injector has associated therewith sense means such as a resistor for generating a voltage indicative of the current flowing to a particular injector. The solenoid control unit comprises; switching circuit means one associated with each injector adapted to receive a particular one of the metering pulses and communicated to a particular sense resistor, the switching circuit means comprises: pull-in signal generating means for generating a pull-in signal in response to a received metering pulse; on/off switch control means for generating an on-control signal during intervals when the injector current is below a predetermined value and for generating an off-control signal when the injector current is above a predetermined value; and a voltage source network means responsive to the pull-in signal for generating a first current reference level signal during the interval at the pull-in signal as present and for thereafter generating a second voltage level reference signal of lower magnitude during the interval thereafter.
The solenoid control unit further includes: pulsed switching type boost voltage generator means responsive to each individual pull-in signal for generating and for storing a boost voltage signal in excess of the voltage established by the battery in synchronism with the generation of each pull-in pulse; and hybrid power circuit means, one associated with each injector and responsive to the boost voltage signal, the on-control signal and the off-control signal for communicating to the injector the boost voltage signal or battery potential in response to the on-control signal and for connecting the injector to a degeneration or recirculation circuit to permit the injector current to decay in response to the receipt of the off-control signal.
The driver utilizes comparator circuits throughout to lessen the requirement for accurate gain control and accurate amplifier offsets. Further features of the invention include a diagnostic circuit able to indicate a malfunction in the driver circuit or to indicate a short circuit in one of the injector coils. Another feature of the present invention is the incorporation therein of means to adapt the driver circuit operation in correspondence with the variation of battery voltage thereby maintaining a uniformity in performance over wide ranging battery conditions. Other features include low power dissipation, a limp home feature which increases the duration of a pull-in pulse when the boost voltage cannot be generated, peak current surge reduction and high reliability.
Many other objects, features and purposes of the present invention will become clear from the following detailed description of the drawings.